Promote Motor Learning Research Articles

Assessment of virtual teacher feedback for the recovery of the upper limb after a stroke. Study protocol for a randomized controlled trial.

Enhanced feedback provided by virtual reality has been shown to promote motor learning both in healthy subjects and patients with motor impairments following lesions of the central nervous system. The aim of this study is to evaluate the effect of displaying a virtual teacher as visual feedback to promote the recovery of upper limb motor function after a stroke. The protocol reports the design of a single blind randomized controlled trial (RCT), blinded to outcome assessment. Two different treatments based on virtual reality will be compared: in the “Teacher” group, the patients receive treatment with continuous displaying of a virtual teacher, while in the “No-Teacher” group, the same exercises will be proposed without visualization of a virtual teacher. The Fugl-Meyer upper extremity scale will be considered as the primary outcome, while the Functional Independence Measure scale, Reaching Performance Scale and Modified Ashworth Scale will be considered as secondary outcomes. Moreover, kinematic parameters such as mean duration (seconds), mean linear velocity (cm/s) and smoothness (i.e. number of sub-movements) will be registered when performing standardised tasks. All tests will be performed before and after treatments. Both treatments will last four weeks with a daily session lasting one hour, five days a week (20 overall sessions). This study is designed to systematically assess the influence of using enhanced visual feedback for the recovery of upper limb motor function after a stroke. These findings will help to determine whether the use of a virtual teacher as enhanced visual feedback is effective for promoting better recovery of upper limb motor function over four weeks of post-stroke treatment. Current Controlled Trials registration number: NCT02234531 (registered on 29 August 2014, ClinicalTrials. gov) Kiper P., Zucconi C., Agostini M., Baba A., Dipalma F., Berlingieri C., Longhi C., Tonin P., Turolla A. Assessment of virtual teacher feedback for the recovery of the upper limb after a stroke. Study protocol for a randomized controlled trial. Med Rehabil 2016; 20(3): 13-20. DOI: 10.5604/01.3001.0009.5010

Online and Offline Performance Gains Following Motor Imagery Practice: A Comprehensive Review of Behavioral and Neuroimaging Studies.

There is now compelling evidence that motor imagery (MI) promotes motor learning. While MI has been shown to influence the early stages of the learning process, recent data revealed that sleep also contributes to the consolidation of the memory trace. How such “online” and “offline” processes take place and how they interact to impact the neural underpinnings of movements has received little attention. The aim of the present review is twofold: (i) providing an overview of recent applied and fundamental studies investigating the effects of MI practice (MIP) on motor learning; and (ii) detangling applied and fundamental findings in support of a sleep contribution to motor consolidation after MIP. We conclude with an integrative approach of online and offline learning resulting from intense MIP in healthy participants, and underline research avenues in the motor learning/clinical domains.

A Temporally Controlled Inhibitory Drive Coordinates Twitch Movements during REM Sleep

During REM sleep, skeletal muscles are paralyzed in one moment but twitch and jerk in the next. REM sleep twitches are traditionally considered random motor events that result from momentary lapses in REM sleep paralysis [1-3]. However, recent evidence indicates that twitches are not byproducts of REM sleep, but are in fact self-generated events that could function to promote motor learning and development [4-6]. If REM twitches are indeed purposefully generated, then they should be controlled by a coordinated and definable mechanism. Here, we used behavioral, electrophysiological, pharmacological, and neuroanatomical methods to demonstrate that an inhibitory drive onto skeletal motoneurons produces a temporally coordinated pattern of muscle twitches during REM sleep. First, we show that muscle twitches in adult rats are not uniformly distributed during REM sleep, but instead follow a well-defined temporal trajectory. They are largely absent during REM initiation but increase steadily thereafter, peaking toward REM termination. Next, we identify the transmitter mechanism that controls the temporal nature of twitch activity. Specifically, we show thata GABA and glycine drive onto motoneurons prevents twitch activity during REM initiation, but progressive weakening of this drive functions to promote twitch activity during REM termination. These results demonstrate that REM twitches are not random byproducts of REM sleep, but are instead rather coherently generated events controlled by a temporally variable inhibitory drive.

Motor Learning Made Possible Using a Tool of Applied Psychophysiology: Quantitative Surface Electromyography

Motor learning is achieved when the subject learns to associate “if movement A, then event B occurs.” Before using surface electromyography to promote motor learning, one must establish that the subject is capable of the cause and effect described above otherwise, the failure to learn may be assumed to be due to a failure in the modality used, in this case SEMG. If the subject is truly incapable of motor learning then no treatment approach is going to be successful. In this case study, quantitative surface electromyography is used to help a 7-year-old child with autistic-like behaviors learn to sit with an upright posture on a bench. The child has never shown any capacity to learn by association, that is, if one does behavior A, then B will occur. Not only did she learn, but the learning generalized outside of the treatment area such that she found and maintained an upright sitting posture at home and school without cueing. Having mastered the sitting goal, new goals were established for her treatment. The new goals began 4 weeks after she demonstrated mastery of sitting and there was no indication that her sitting posture had deteriorated in any way. Sitting with a severe back curvature for prolonged periods at this age poses problems for later development of the spine and negatively affects the ability to maintain good breath support for speech therapy.

A review on the mechanical design elements of ankle rehabilitation robot

Ankle rehabilitation robots are developed to enhance ankle strength, flexibility and proprioception after injury and to promote motor learning and ankle plasticity in patients with drop foot. This article reviews the design elements that have been incorporated into the existing robots, for example, backdrivability, safety measures and type of actuation. It also discusses numerous challenges faced by engineers in designing this robot, including robot stability and its dynamic characteristics, universal evaluation criteria to assess end-user comfort, safety and training performance and the scientific basis on the optimal rehabilitation strategies to improve ankle condition. This article can serve as a reference to design robot with better stability and dynamic characteristics and good safety measures against internal and external events. It can also serve as a guideline for the engineers to report their designs and findings.

Effects of transcranial direct current stimulation on motor learning in healthy individuals: a systematic review

Introduction Transcranial direct current stimulation (tDCS) has been used to modify cortical excitability and promote motor learning. Objective To systematically review published data to investigate the effects of transcranial direct current stimulation on motor learning in healthy individuals. Methods Randomized or quasi-randomized studies that evaluated the tDCS effects on motor learning were included and the risk of bias was examined by Cochrane Collaboration’s tool. The following electronic databases were used: PubMed, Scopus, Web of Science, LILACS, CINAHL with no language restriction. Results It was found 160 studies; after reading the title and abstract, 17 of those were selected, but just 4 were included. All studies involved healthy, right-handed adults. All studies assessed motor learning by the Jebsen Taylor Test or by the Serial Finger Tapping Task (SFTT). Almost all studies were randomized and all were blinding for participants. Some studies presented differences at SFTT protocol. Conclusion The result is insufficient to draw conclusions if tDCS influences the motor learning. Furthermore, there was significant heterogeneity of the stimulation parameters used. Further researches are needed to investigate the parameters that are more important for motor learning improvement and measure whether the effects are long-lasting or limited in time.

Neurological Rehabilitation: Optimizing Motor Performance

This second edition of Neurological Rehabilitation: Optimizing Motor Performance provides a practical, task-oriented approach to rehabilitation for clients with neurological conditions, emphasizing active participation by clients and providing details of exercises and training to challenge them and help them regain the strength and endurance needed for independent living. In the new edition, authors Janet Carr and Roberta Shepherd have included updated scientific evidence as well as input from colleagues whose research and clinical expertise are also in this area of practice. Neurological Rehabilitation is also innovative in discussing the need to expand rehabilitation to increase opportunities for practice by including semi-supervised groups and circuit training in addition to traditional one-to-one interventions. The book is divided into three parts. Chapters 1–3 provide a foundation for understanding the role of neuro-rehabilitation in recovery. Chapter 1 reviews plasticity in the brain and the role of practice and challenge in brain reorganization; chapter 2 builds on this by discussing task-specific practice, the principles of motor learning, and clinical applications of these principles in neuro-rehabilitation. Chapter 3 provides an overview of measurement tools commonly used in neuro-rehabilitation. Part 2 devotes one chapter to each of the following specific actions required for independent living: standing up and sitting down, walking, reaching and manipulation, and balancing. Each chapter describes the action and the biomechanical factors, the motor dysfunction that occurs following neurological injury, and practical methods for training, focusing on repetitive task-oriented training, functional strength training of task-related muscles, and maximizing skills with practice and variety. The information on training is applicable to patient care, but because it focuses on clients who are able to perform the action, there is less guidance for working with those who are unable to do so, or who need to work on other tasks such as getting out of bed. Part 3 covers lesions to the motor and sensory–perceptual systems and includes detailed chapters on stroke, traumatic brain injury, Parkinson's disease, and multiple sclerosis. Each chapter discusses the pathology of the lesion or condition, resulting clinical features, training, and specific assessments. The recommended management consistently includes specific exercises and task-specific and aerobic training. Throughout, Carr and Shepherd also provide information on supplementary methods for rehabilitation, including mental practice, orthosis, electrostimulation, and computerized aids, and discuss the evidence-based benefits of including these methods in management strategies. Photos of exercises, clients, and clinicians working with clients complement the text and are helpful for applying the information clinically. Neurological Rehabilitation: Optimizing Motor Performance is an excellent book for a practical, task-oriented approach to neuro-rehabilitation, and I would recommend it as one of the key resources for working with clients with neurological conditions. However, additional resources may also be useful, since this book focuses on the task-oriented approach and offers little information or evidence on other approaches. Because of its rehabilitation focus, Neurological Rehabilitation will be most beneficial to physical therapy students, new graduates and experienced clinicians who work in neuro-rehabilitation, but other health care professionals and physical therapists in other settings may also find it helpful for the detailed information it provides on neurological injury and recovery. Overall, Neurological Rehabilitation balances evidence with clinical application, provides a foundation of knowledge for neuro-rehabilitation as well as methods for promoting motor learning and plasticity, and encourages readers to think about changing the delivery of therapy to enhance learning and recovery.

Non-physical practice improves task performance in an unstable, perturbed environment: motor imagery and observational balance training.

For consciously performed motor tasks executed in a defined and constant way, both motor imagery (MI) and action observation (AO) have been shown to promote motor learning. It is not known whether these forms of non-physical training also improve motor actions when these actions have to be variably applied in an unstable and unpredictable environment. The present study therefore investigated the influence of MI balance training (MI_BT) and a balance training combining AO and MI (AO+MI_BT) on postural control of undisturbed and disturbed upright stance on unstable ground. As spinal reflex excitability after classical (i.e., physical) balance training (BT) is generally decreased, we tested whether non-physical BT also has an impact on spinal reflex circuits. Thirty-six participants were randomly allocated into an MI_BT group, in which participants imagined postural exercises, an AO+MI_BT group, in which participants observed videos of other people performing balance exercises and imagined being the person in the video, and a non-active control group (CON). Before and after 4 weeks of non-physical training, balance performance was assessed on a free-moving platform during stance without perturbation and during perturbed stance. Soleus H-reflexes were recorded during stable and unstable stance. The post-measurement revealed significantly decreased postural sway during undisturbed and disturbed stance after both MI_BT and AO+MI_BT. Spinal reflex excitability remained unchanged. This is the first study showing that non-physical training (MI_BT and AO+MI_BT) not only promotes motor learning of “rigid” postural tasks but also improves performance of highly variable and unpredictable balance actions. These findings may be relevant to improve postural control and thus reduce the risk of falls in temporarily immobilized patients.

Neuroplasticity of imagined wrist actions after spinal cord injury: a pilot study.

Motor imagery (MI - i.e., the mental representation of an action without physically executing it) stimulates brain motor networks and promotes motor learning after spinal cord injury (SCI). An interesting issue is whether the brain networks controlling MI are being reorganized with reference to spared motor functions. In this pilot study, we tested using magnetoencephalography (MEG) whether changes in cortical recruitment during MI were related to the motor changes elicited by rehabilitation. Over a 1-year period of inclusion, C6 SCI participants (n = 4) met stringent criteria for inclusion in a rehabilitation program focused on the tenodesis prehension (i.e., a compensatory prehension enabling seizing of objects in spite of hand and forearm muscles paralysis). After an extended baseline period of 5 weeks including repeated MEG and chronometric assessments of motor performance, MI training was embedded to the classical course of physiotherapy for five additional weeks. Posttest MEG and motor performance data were collected. A group of matched healthy control participants underwent a similar procedure. The MI intervention resulted in changes in the variability of the wrist extensions, i.e., a key movement of the tenodesis grasp (p < .05). Interestingly, the extent of cortical recruitment, quantified by the number of MEG activation sources recorded within Brodmann areas 1-8 during MI of the wrist extension, significantly predicted actual movement variability changes across sessions (p < .001). However, no such relationship was present for movement times. Repeated measurements afforded a reliable statistical power (range .70-.97). This pilot study does not provide straightforward evidence of MI efficacy, which would require a randomized controlled trial. Nonetheless, the data showed that the relationship between action and imagery of spared actions may be preserved after SCI.

Influence of treadmill training in dual-task gait in people with Parkinson's Disease: a case report

The loss in the automaticity of gait hinders the performance of concurrent activities - Dual Task (DT) - in individuals with Parkinson's disease (PD). One hypothesis for the negative interference of DT on gait is related to the limitation of attention resources in the brain for different activities. When the automation of a task occurs, the negative interference of DT on the gait can be minimized. Because the treadmill promotes automaticity of a better locomotion pattern, due to the repetition that promotes motor learning, the study sought to investigate whether treadmill training can improve the performance of gait on DT in people with PD. Three individuals were evaluated in the on-phase of the antiparkinsonian medication regarding the kinematics (Qualisys Motion Capture System) while in gait, simultaneously performing cognitive activities. Subsequently, the subjects performed a 20-minute workout on the treadmill and were reassessed during gait in cognitive activities. There were increases in the length of the cycle (p=0.01), the length of the step (p=0.01) and in total swing time (p=0.03), and a decrease in the total length of support (p=0.03). These results indicate that treadmill training can promote improvement in the performance of DT on gait in individuals with PD. Longitudinal studies with this focus of research are needed.

Re-thinking the role of motor cortex: Context-sensitive motor outputs?

The standard account of motor control considers descending outputs from primary motor cortex (M1) as motor commands and efference copy. This account has been challenged recently by an alternative formulation in terms of active inference: M1 is considered as part of a sensorimotor hierarchy providing top–down proprioceptive predictions. The key difference between these accounts is that predictions are sensitive to the current proprioceptive context, whereas efference copy is not. Using functional electric stimulation to experimentally manipulate proprioception during voluntary movement in healthy human subjects, we assessed the evidence for context sensitive output from M1. Dynamic causal modeling of functional magnetic resonance imaging responses showed that FES altered proprioception increased the influence of M1 on primary somatosensory cortex (S1). These results disambiguate competing accounts of motor control, provide some insight into the synaptic mechanisms of sensory attenuation and may speak to potential mechanisms of action of FES in promoting motor learning in neurorehabilitation.

Use of the Challenge Point Framework to Guide Motor Learning of Stepping Reactions for Improved Balance Control in People With Stroke: A Case Series

Stepping reactions are important for walking balance and community-level mobility. Stepping reactions of people with stroke are characterized by slow reaction times, poor coordination of motor responses, and low amplitude of movements, which may contribute to their decreased ability to recover their balance when challenged. An important aspect of rehabilitation of mobility after stroke is optimizing the motor learning associated with retraining effective stepping reactions. The Challenge Point Framework (CPF) is a model that can be used to promote motor learning through manipulation of conditions of practice to modify task difficulty, that is, the interaction of the skill of the learner and the difficulty of the task to be learned. This case series illustrates how the retraining of multidirectional stepping reactions may be informed by the CPF to improve balance function in people with stroke. Four people (53-68 years of age) with chronic stroke (>1 year) and mild to moderate motor recovery received 4 weeks of multidirectional stepping reaction retraining. Important tenets of motor learning were optimized for each person during retraining in accordance with the CPF. Participants demonstrated improved community-level walking balance, as determined with the Community Balance and Mobility Scale. These improvements were evident 1 year later. Aspects of balance-related self-efficacy and movement kinematics also showed improvements during the course of the intervention. The application of CPF motor learning principles in the retraining of stepping reactions to improve community-level walking balance in people with chronic stroke appears to be promising. The CPF provides a plausible theoretical framework for the progression of functional task training in neurorehabilitation.

Independent Mobility After Early Introduction of a Power Wheelchair in Spinal Muscular Atrophy

Weakness resulting from spinal muscular atrophy causes severe limitations in functional mobility. The early introduction of power mobility has potential to enhance development and mitigate disability. These outcomes are achieved by simulating normal skill acquisition and by promoting motor learning, visuospatial system development, self-exploration, cognition, and social development. There are few reports on early power mobility in spinal muscular atrophy, and it is typically not prescribed until school age. The authors evaluated 6 children under age 2 years with neuromuscular disease (5 spinal muscular atrophy, 1 congenital muscular dystrophy) for power mobility. Parents recorded the practice hours necessary to achieve independence using the Power Mobility Skills Checklist. Four children achieved independence in all items on the checklist by 7.9 months (range: 73-458 days). Introduction of early power mobility is feasible in spinal muscular atrophy patients under age 2 years and should be introduced in late infancy when children typically acquire locomotor skills.

Feedback and intention during motor-skill learning: a connection with prospective memory

The intention to complete an action in the future can improve the learning of this action, but it is unknown whether this effect persists when feedback is manipulated during encoding. In experiment 1, participants were instructed to learn a motor skill with or without intending to reproduce this learning in the future, and feedback on their movements was administrated by self-decision, that is, participants asked for feedback whenever they wanted it. The results showed that intention increased the frequency with which feedback was requested, but did not improve motor performance. In experiment 2, participants had to learn the task with high or few feedbacks, which they could not control. In these conditions, intention was beneficial in promoting motor learning only for a low feedback schedule. We suggest that the beneficial effect of intention on learning can be overshadowed or emphasised by the feedback processing during encoding. These findings are discussed in light of theories surrounding prospective memory.

Script Training Treatment for Adults With Apraxia of Speech

Outcomes of script training for individuals with apraxia of speech (AOS) and mild anomic aphasia were investigated. Script training is a functional treatment that has been successful for individuals with aphasia but has not been applied to individuals with AOS. Principles of motor learning were incorporated into training to promote long-term retention of scripts. Three individuals with AOS completed script training. A multiple-baseline, across-behaviors design examined acquisition of client-selected scripts. Errors and speaking rates were also analyzed. Random practice and delayed feedback were incorporated into training to promote motor learning. Probes for long-term retention were elicited up to 6 months after treatment. All clients successfully acquired their scripts, and probes demonstrated script retention 6 months after treatment. Errors generally decreased but remained variable even during maintenance and retention probes. Speaking rate increased for 2 clients but also remained variable. Script training was successful and functional for clients with AOS. Clients reported increased confidence, speaking ease, and speech naturalness. Although scripts did not become errorless, clients retained their scripts and reported using them frequently. Whether principles of motor learning may have promoted the long-term retention of scripts exhibited by participants must be determined through future research.

Feasibility of an Intensive Trial of Modern Dance for Adults with Parkinson Disease

Although preliminary evidence supports the psychophysical benefits of dance for adults with Parkinson disease, guidelines for community-based dance programs await further scrutiny for safety and efficacy. This pilot study was designed to assess the feasibility of an intensive trial of group-delivered modern dance for 11 adults with early-to-middle stage Parkinson’s. The Timed ‘‘Up and Go’’ test and the Fullerton Advanced Balance scale were administered to assess balance safety and re-administered at closure along with a self-reported feedback questionnaire. Video recordings were analyzed for qualitative behavioral change. Pre/posttest comparisons from the Timed ‘‘Up and Go’’ test were not significant, while those from the Fullerton Advanced Balance Scale were significant at the .05 level for the group as a whole (p = .01) with an average score change of +3.1 points. Although qualitative results generally concurred with the social benefits associated with an enjoyable form of expressive exercise, important indicators surfaced bearing on future research and community program designs. These include need for more rigorous stratification of participants and adapting dance class structure to address specific group needs to promote motor learning for sustained functional gains.

Neuromagnetic imaging of movement-related cortical oscillations in children and adults: Age predicts post-movement beta rebound

We measured visually-cued motor responses in two developmentally separate groups of children and compared these responses to a group of adults. We hypothesized that if post-movement beta rebound (PMBR) depends on developmentally sensitive processes, PMBR will be greatest in adults and progressively decrease in children performing a basic motor task as a function of age.Twenty children (10 young children 4–6 years; 10 adolescent children 11–13 years) and 10 adults all had MEG recorded during separate recordings of right and left index finger movements.Beta band (15–30 Hz) event-related desynchronization (ERD) of bi-lateral sensorimotor areas was observed to increase significantly from both contralateral and ipsilateral MI with age. Movement-related gamma synchrony (60–90 Hz) was also observed from contralateral MI for each age group. However, PMBR was significantly reduced in the 4–6 year group and, while more prominent, remained significantly diminished in the adolescent (11–13 year) age group as compared to adults. PMBR measures were weak or absent in the youngest children tested and appear maximally from bilateral MI in adults. Thus PMBR may reflect an age-dependent inhibitory process of the primary motor cortex which comes on-line with normal development.Previous studies have shown PMBR may be observed from MI following a variety of movement-related tasks in adult participants – however, the origin and purpose of the PMBR is unclear. The current study shows that the expected PMBR from MI observed from adults is increasingly diminished in adolescent and young children respectively. A reduction in PMBR from children may reflect reduced motor cortical inhibition. Relatively less motor inhibition may facilitate neuronal plasticity and promote motor learning in children.

Does Sleep Promote Motor Learning? Implications for Physical Rehabilitation

Sleep following motor skill practice has repeatedly been demonstrated to enhance motor skill learning off-line (continued overnight improvements in motor skill that are not associated with additional physical practice) for young people who are healthy. Mounting evidence suggests that older people who are healthy fail to demonstrate sleep-dependent off-line motor learning. However, little is known regarding the influence of sleep on motor skill enhancement following damage to the brain. Emerging evidence suggests that individuals with brain damage, particularly following stroke, do benefit from sleep to promote off-line motor skill learning. Because rehabilitation following stroke requires learning new, and re-learning old, motor skills, awareness that individuals with stroke benefit from a period of sleep following motor skill practice to enhance skill learning could affect physical therapist practice. The objective of this article is to present the evidence demonstrating sleep-dependent off-line motor learning in young people who are healthy and the variables that may influence this beneficial sleep-dependent skill enhancement. In young people who are healthy, these variables include the stages of memory formation, the type of memory, the type of instruction provided (implicit versus explicit learning), and the task utilized. The neural mechanisms thought to be associated with sleep-dependent off-line motor learning also are considered. Research examining whether older adults who are healthy show the same benefits of sleep as do younger adults is discussed. The data suggest that older adults who are healthy do not benefit from sleep to promote off-line skill enhancement. A possible explanation for the apparent lack of sleep-dependent off-line motor learning by older adults who are healthy is presented. Last, emerging evidence showing that individuals with chronic stroke demonstrate sleep-dependent off-line motor skill learning and some of the possible mechanisms for this effect are considered.

Effect of self-controlled knowledge of results in motor skill learning of elderly adults

The aim of this study was to analyze the effects of self-controlled knowledge of results (KR) in motor skill learning of elderly adults. Twenty subjects (65.45 + 5.34 years-old), inexperienced in the required task, were randomly distributed in two experimental groups: 1) Self-controlled Group, who received KR whenever requested; 2) Yoked Group, who received KR on the same trials of the Self-controlled Group. The task consisted of moving three tennis balls into six roles, positioned in a wood platform, in a previously determined sequence and target time. During the acquisition phase, the subjects performed 45 trials with a target time of 4500 ms. The immediate transfer tests, conducted ten minutes after the acquisition phase, consisted of 45 trials with a target time of 5000 ms. After forty eight hours, the same procedure was conducted for the latest transfer test. The results showed marginal differences, suggesting a higher performance of self-controlled group. It was concluded that selfcontrolled KR is helpful to promote motor learning in elderly adults.

The Effects of Observational Feedback and Verbal Cues on the Motor Learning of an Aimed Reach-and-Point Task

Current technology allows the recording of movement for both motion analysis and providing observational feedback. The most effective type of observational feedback is under debate. We compared a child's reach-and-point performance after viewing a videotaped playback of a model's performance and after viewing a split-screen comparison of the model's and child's performances while simultaneously receiving verbal cues. A PTVision system provided observational feedback and recorded spatial trajectory, target accuracy, movement time, and joint angles while a 13 year-old boy with cerebral palsy reached for three targets. The split-screen comparison had the largest effect on reach performance, including slower-yet-more-accurate movements and a more extended wrist, curved spatial trajectories, and an ulnar-deviated wrist. Feedback using split-screen comparison between a model's and the child's performance with verbal cues appears to promote motor learning. When using technology to augment therapy, the intervention should be designed considering current motor learning principles.